The atomic layer controlled growth or atomic layer deposition (ALD) of single-element films is important for thin film device fabrication [1]. As component sizes shrink to nanometer dimensions, ultrathin metal films are necessary as diffusion barriers to prevent interlayer and dopant diffusion [2]. Conformal metal films are needed as conductors on high aspect ratio interconnect vias and memory trench capacitors [3]. The ALD of single-element semiconductor films may also facilitate the fabrication of quantum confinement photonic devices [4].
Currently, most thin metal films are formed by a chemical vapor deposition (CVD) method. However, the CVD process often results in pin-holes, gaps and/or defects on the surface. Furthermore, the resulting thin metal film surface is often rough and has uneven metal film thickness.
While thin films of a variety of binary materials can be grown with atomic layer control using sequential self-limiting surface reactions [5,6], thin film of metal using ALD has not been successful achieved. For example, ALD technique has recently been employed to deposit a variety of binary materials including oxides [7-11], nitrides [12,13], sulfides [14,15] and phosphides [16]. In contrast, the atomic layer growth of single-element, e.g., metal, films has never been achieved using this approach. Earlier efforts to deposit copper with atomic layer control were unsuccessful because the surface chemistry was not self-limiting and the resulting copper films displayed coarse polycrystalline grains [17,18]. Previous attempts to achieve silicon ALD with sequential surface chemistry could not find a set of reactions that were both self-limiting [19]. Germanium ALD has been accomplished using self-limiting surface reactions only in conjunction with a temperature transient [20].
Therefore, there is a need for a method for forming a thin metal film layer on a solid material surface using a plurality of self-limiting reactions.